Dear Technical Support Team,
I am using the NB671LAGQ-Z in my design to generate a 5V output. However, I am experiencing significant triangular ripple on the output under light or no-load conditions. The ripple persists regardless of the state of the LP pin.
I have attached the schematic and an oscilloscope waveform of the output for your reference.
Could you please provide guidance on the possible cause of this behavior and how to reduce the ripple to acceptable levels?
Thank you for your support.
Hello scoteedimc9,
I just wanted to let you know that this device is not recommended for new designs. In the NB671LA datasheet the NB671LC and NB691A are mentioned as alternatives. Please reach out here if interested in a datasheet for these alternatives:
https://www.monolithicpower.com/en/support/mps-now.html
That being said I think this behavior at light or no load conditions arises as a result of the skip mode that occurs during these conditions. This skip mode feature reduces the frequency and is described on page 10 and 11.
Ways to reduce this would be to increase the capacitance used.
Dear Eduardo Munoz,
I wanted to share the steps I took to reduce the output ripple on my PCB and optimize its performance. Initially, the PCB had significant ripple issues due to the use of tantalum capacitors, which had high ESR and ESL. To address this, I replaced the tantalum capacitors with four 22µF ceramic capacitors in parallel. This change improved the filtering and reduced the ripple. Later, I further optimized the design by replacing the 22µF capacitors with four 100µF ceramic capacitors. This adjustment provided even better filtering, resulting in the ripple decreasing to 68mV peak-to-peak.
I have attached oscilloscope waveforms of the output signal to demonstrate the improvements achieved. Additionally, I recommend reviewing the following resource from Texas Instruments for further insights into understanding, measuring, and reducing output noise in DC/DC switching regulators:
Understanding, Measuring, and Reducing Output Noise in DC/DC Switching Regulator.
Best regards,
Ruslan Muradov
